The following hypotheses will be tested: a) screening for prostate cancer with digital rectal exam and PSA blood test will reduce the mortality from prostate cancer; b) screening for lung cancer with chest x-ray will reduce mortality from lung cancer; c) screening for colorectal cancer with sigmoidoscopy will reduce mortality from colorectal cancer, and d) screening for ovarian cancer with transvaginal ultrasound and CA-125 will reduce mortality from ovarian cancer. All subjects will be age 55 - 74.